SignificanceSatellite altimetry has shown that global mean sea level has been rising at a rate of ∼3 ± 0.4 mm/y since 1993. Using the altimeter record coupled with careful consideration of interannual and decadal variability as well as potential instrument errors, we show that this rate is accelerating at 0.084 ± 0.025 mm/y2, which agrees well with climate model projections. If sea level continues to change at this rate and acceleration, sea-level rise by 2100 (∼65 cm) will be more than double the amount if the rate was constant at 3 mm/y.

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In 1978, during the last 25 days of the SEASAT mission, the satellite ground tracks repeated within 2.5 km every 3 days. This yielded eight to nine sets of global collinear altimeter data with a cross-track grid spacing of approximately 900 km at the equator and 600 km at mid-latitude. Because the geoid is time-invariant, such observations can reveal sea surface height variability due to dynamic ocean phenomena. We have solved for variations due to deep-ocean mesoscale features by eliminating the longer wavelength deviations. Modeled tidal heights were first subtracted from the altimeter data, and linear trends were then removed from collinear segments approximately 2000 km in length. This second step eliminates relative orbit error together with any residual tide model errors. The resulting sea height profiles have a precision of a few centimeters, and the global variability map constructed from these data reveals a strikingly realistic view of mesoscale energetics. Maximum values of 20-40 cm rms variability are generated by meanders and eddies of five major current systems: Gulf Stream, Kuroshio, Agulhas, Antarctic Circumpolar, and Falkland/Brazil confluence. Perhaps a more significant discovery was the dominance of exceedingly small variability over vast regions of the oce•/ns; approximately 70% of all global values were less than 5 cm. This category included the eastern North Pacific, eastern South Pacific, and almost the entire South Atlantic where values as small as 1-2 •m were common. With such a low level of background noise, even some currents with relatively small sea height signatures could be detected. In both the Atlantic and the Pacific, for example, the North Equatorial Current systems were clearly expressed as zonal bands of higher variability. 4343 surement capability of satellite altimeters. Geoid-independent techniques have therefore been developed to determine sea height variability from altimeter data'. One of these is the 'crossover difference' approach, in which altimeter measurements are evaluated at intersections of ascending and descending ground tracks. At the crossing point, the static part of the ocean surface height caused by the geopotential contribution is the same on both tracks and can thus be eliminated by a simple difference of the two measurements. When altimetric analyses are restricted to the deep ocean, long wavelength signals due to orbit error and tides can be separated from those due to mesoscale features, and variability of the eddy field is obtained. Maps of variability produced from dense gr'fd• of altimetric data can thus be used to characterize the m•eS0scale energetics of a region or to monitor paths of currents. Application of this concept has been demonstrated by using SEASAT altimeter data in the North Pacific [Marsh et al., 1982] and GEOS 3 data in the North Atlantic [Cheney and Marsh, 1981b]. In the latter case, the altimetric map of sea height variability clearly delineated the energetic Gulf Stream• meander domain in contrast to the less variable background ...

[1] Mean sea level trends from TOPEX and Jason-1 altimeter data are recomputed using unified geophysical modeling and the new ITRF2005 terrestrial reference frame for the entire altimetric time series, with consistent orbits based on satellite laser ranging (SLR) and DORIS tracking data. We obtain a global rate of 3.36 ± 0.41 mm/yr over the 14 year period from 1993 to 2007. The regional sea level trends computed with the new reference frame show significant north/south hemispherical offsets of ±1.5 mm/yr relative to trends based on the previous 1995-era frame.